Devices to improve the thermal efficiency of existing fireplaces are old in the art. One such device, shown by Nelson, U.S. Pat. No. 4,068,650, comprises a metal air conveying channel fitting closely against the inside walls of the existing fireplace. The interior of the channel contains an electric blower or the like, directing room air to be heated toward and through multiple horizontal passages or baffles contained within the channel. After the air has been heated it is subsequently discharged into the room. Devices of the type employing blowers and baffles have several disadvantages. Intially, any savings in energy achieved by using these devices to improve the thermal efficiency of the fireplace may be offset by the power required to operate the electric blowers within the channel. In addition, when in operation the blowers may create undesirable noise caused either by the blower motor or the vibration of the blower within the interior of the channel. The multiple horizontal passages contained within the channel make the device difficult to manufacture and install. These devices typically include a structural component placed over the fire to deflect the fire from its normal upward path. The structure typically hampers routine inspection and cleaning of the chimney which is necessary to prevent dangerous chimney fires. Further, these structures provide additional surface areas for the accumulation of uncombusted fire residules such as creosotes or the like. Thus, the inclusion of these structures mandates the total removal of the unit from the parent fireplace to permit the performance of these necessary preventative safety measures.
Another device insertable into an existing fireplace is shown by Wolcott, U.S. Pat. No. 886,453. The device generally comprises an open grate enclosed around the back and sides by hollow walls. Within the walls are a plurality of vertical and horizontal partitions giving the walls structural support. These partitions also define a plurality of compartments within the walls. Openings within the partitions allow room air to circulate behind the grate between adjacent compartments where it is heated and discharged back into the room. This device, and devices similar to this device, have several disadvantages. The limited openings within the partitions restrict the amount of room air which can be heated by the device thereby limiting any improvement in thermal efficiency. The hollow walls with the internal vertical and horizontal partitions, produce a device which is both difficult to manufacture and heavy. As a result, this device is not easily installed into a fireplace.
The present invention overcomes these problems of the prior art. By utilizing an air passage defined by the existing fireplace bottom, rear wall, and side walls, and the bottom, rear wall and side walls of a convection chamber insertable into the fireplace, the present invention heats the natural flow of room air drawn under and behind the convection chamber, and discharges it into the room. The present invention does not include any obstruction between the fire and the chimney. This allows the inspection and cleaning of the chimney without removal of the unit and minimizes the areas upon which uncombusted fire residues may accumulate. In that the present invention makes use of the existing fireplace structure, it is mechanically simple, easily constructed, and easily inserted into the fireplace without penetrating or in any manner damaging the existing fireplace structure. Due to the mechanical simplicity of the convection chamber the present invention does not detract from the aesthetic appearance of the existing fireplace.